Recently, with an increased density and enhanced function of an electronic circuit board, attention has been paid to a component-embedded substrate having a structure in which electronic components are embedded in an insulating substrate serving as an insulating layer. With a wiring pattern formed on a surface of the insulating substrate, the component-embedded substrate can be used as a module board on the surface of which various electronic components are mounted in a predetermined position of the wiring pattern and can also be used as a core board for use in manufacturing a component-embedded multilayer circuit board by a buildup method.
The aforementioned component-embedded substrate requires an electrical connection between the wiring pattern and the terminals of the electronic components in the insulating substrate. It has been known to use soldering for the connection (for example, see Patent Document 1).
In the meantime, several surface mounting processes of various electronic components are performed in the process of manufacturing the module board or the multilayer circuit board. In general, reflow soldering is performed for the surface mounting of the electronic components. Each time an electronic component is mounted, the component-embedded substrate is placed in a reflow furnace and is heated to a temperature at which the solder melts. Therefore, the connection portion between the wiring pattern and the terminals of the intra-substrate electronic components in the component-embedded substrate disclosed in Patent Document 1 is heated to a solder melting temperature several times, which may reduce the reliability of the connection portion.
In light of this, in order to improve the reliability of the connection portion in the component-embedded substrate, it has been known to provide electrical connections between the terminals of the intra-substrate electronic components and the wiring pattern on the surface of the substrate by copper plating. Specifically, the melting point of copper is higher than the melting point of the solder, and thus the component-embedded substrate placed in the reflow furnace does not allow the connection portion to melt, thereby maintaining the reliability of the connection portion.
For example, as an aspect of the method of manufacturing a component-embedded substrate by electrically connecting the terminals of the intra-substrate electronic components to the wiring pattern on the surface of the insulating substrate using such a copper plating method, there has been known a component-embedded substrate manufacturing method disclosed in Patent Document 2.
Here, the following description focuses on the component-embedded substrate manufacturing method as exemplified by Patent Document 2.
First, a lamellar body is formed by laminating an insulating layer on a metal layer such as a copper foil, and a guide hole is provided in the lamellar body. Then, a connection hole is provided in a component arrangement region in which an intra-substrate component is expected to be arranged in the lamellar body using the guide hole as a reference. In a later step, the connection hole is to be filled with copper to form a metal joint for electrically connecting the wiring pattern to the terminal of the intra-substrate component. Therefore, the connection holes are provided for the number of the terminals corresponding to the places in which the terminals of the intra-substrate components are expected to be positioned. Then, an adhesive is applied to the component arrangement region and the adhesive is used to fix the intra-substrate components. At this time, the intra-substrate components are positioned using the connection holes. Then, the lamellar body having the intra-substrate components placed therein is laminated with an insulating base material such as a prepreg to form an insulating substrate having the intra-substrate components embedded therein. The obtained insulating substrate has the metal layer located on one surface thereof and the connection hole is opened in a predetermined position of the metal layer. In this state of the insulating substrate, the adhesive is removed from within the connection holes to expose the terminal of the intra-substrate component in the connection hole, and then the entire insulating substrate is subjected to a copper plating process. This causes copper to grow and fill the connection hole so as to electrically connect the metal layer on the surface of the insulating substrate to the terminal of the intra-substrate component. Subsequently, part of the metal layer on the surface of the insulating substrate is etched to form a wiring pattern and thereby to form a component-embedded substrate.